Control system for electric motors.



H. L. BEACH. CONTROL SYSTEM FOR ELECTRIC MOTORS.

APPLICATION FILED iUNE 9.19:4.

1,157.2(33. Patented Oct. 19, 1915.

WWN sEs: INVENTOR Howard L. Beach.

i) BY ATTORNEY UNITED STATES PATENT OFFICE. I

' HOWARD L. BEACH, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVAN IA.

CONTROL SYSTEM FOR ELECTRIC MOTORS;

To all whom it may concern:

Be it known that L'HowAnn L. BEACH, a citizen of the United States, and a resident of Edgewood Park, in the county of Alle- 5 gheny and State of Pennsylvania, have in vented a new and useful Improvement in Control Systems for Electric Motors, of which the following is a specification.

My invention relates to control systems 10 for electric motors and it has particular reference to such systems as embody motors that are adapted to operate at variable speed. My'invention has for its object to provide a simple and efiiciert means for automati cally' controlling the acceleration of an electric motor by varying the voltage of its supply circuit. With few exceptions, the many systems for controlling the acceleration of electric motors that have been proposed hitherto, ineludea sectional resistor and a number of switches for controlling it. While this form of control may lee-necessary in some installations, it has been found that the same results may be obtained by other and simpler means when it is possible to control the voltage of the source of energy. For example, in the operation of paper machines or similar mechanisms which are driven by single motors that are supplied with energy by separate generatorslocated adjacent to the motors, the voltage of the generator may be varied to control the acceleration of the paratus embodying my invention. Fig. 2 is a View, similar to Fig. 1, of a modification.

A generator 1 is connected in series with a motor 2 to which'it supplies energy. The generator 1. and the motor 2 are respectively provided with field windings 3 and 4 that are separately excited by any suitable source of energy at constant voltage. The excitalJlOIl'Of the field windings 3 and 1 may be controlled by variable resistors 5 and 6 which may be adjusted to produce any desired field strength. The resistors 5 and 6 Specification of Letters Patent.

Application filed June 9, 1914. Serial No. 843,915.

are controlled by an electromagnetic switch 7 having an actuating coil 8, that is connected across the terminals of the generator, and by electromagnetic switches 9 and 10, whose coils 11 and 12 are in series with the armature windings ofthe motor 2. A threepole double-throw switch 13, which may, if desired, be replaced by electromagnetic switches, operates to control the main circuit.

It may be assumed thatthe system above described, which has been in operation at the desired speed, is stationary, and that it is desired to start the motor and cause it to operate at the same speed as before. Before the main switch 13 is closed, the voltage of the generator will be low because the' resistor 5 is in series with the field windings 3. The switch 7 is in its lower position, and the switches 9 and 10 are respectively in closed and in open positions since the motor circuit is open. When the switch 13 is closed, the switch blade 14 completes a circuit which includes the switch 9 for shunting the resistor 5. The consequent rise in generator voltage because of the increased excitation of the field windings 3 causes a rush of current in the main circuit. The coil 11 is energized to open the switch 9 and thereby remove the shunt for the resistor 5 and thus decrease the voltage of the generator. The switch 9 then oscillates in the same manner as the well known field-accelerating or fluttering relay to bring the generator voltage gradually up to its full value. \Vhen the generator voltage reaches its normal value, the coil 8 will be sufiiciently encrgized to raise the switch 7 which, in its lower position, has completed a. shunt for the resistor 6, thereby insuring a strong field for the motor 2 in starting- The operation of the switch 7 servesto remove the shunt for the resistor 6, and the-motor field is accordinglyweakened. A rush of current ocours in the main circuit, and the coil .12 is energized to close the switch 10 and\thus complete a shunt circuit for the resistor 6.

When the motor has been accelerated to follow the opening of the switch and the coil 12 will be suliiciently energized to again close the switch. 10 which will oscillate, in the same manner as that described in conncction with the switch 9, to gradually accelerate the motor to its normal running speed with the resistor 6 in series with the field windings 4'.

When it is desired to stop the motor, it is only necessary to reverse the position or the switch 18, whereupon the switch blade 15 will engage a contact member 16 to close a dynamic braking circuit for the motor, through a suitable resistor 17, and the motor will be brought to rest safely and quickly.

It will be noted that, in the above system, it is impossible to connect the motor to the generator when the generator voltage is high or when the motorfield is weak. It is also impossible to close the dynamicbraking circuit while the motor is connected to the.

generator.

A modification is illustrated in Fig. 2 in which similar numerals are employed to designate corresponding parts. A main switch 18 and 'a switch 19 for controlling a shunt circuit for the resistor 5 are respectively provided with actuating coils 20 and 21 that are controlled'by a snap switch 22. The double-throw switches 23 and at, which control the shunt circuits for the resistors 5 and 6, are in their lower positions when the system is not in operation. The resistor 6 is short circuited, thus insuring a strong field for the motor 2 in starting.

When the switch 22 is closed, the coils 20 and 21 are energized to close the switches 18 and 19. When the switch 19 closes, a short circuit is completed for the resistor The voltage of the generator is accordingly increased, and a rush of current occurs in the main circuit. The coil of the switch 24 is sui'iiciently energized to raise the switch to open a shunt circuit for the resistor 5 and thereby decrease the field excitation of the generator 1. The switch 24- then drops to its lower position to again complete the shunt circuit for the resistor and cause a second rush of current in the main circuit. The switch 2i then operates as a fluttering relay to gradually bring the generator voltage to its normal value. \Vhen' the generator voltage reaches a predetermined value, the coil 26 of the switch 23 is sui'licicntly cncrgized to raise the switch to its upper position to maintain a shunt circuit for the resistor 5 and to openthe shunt circuit for the resistor (5. The resulting weakening ot' -thc motor lield causes a rush of current in the main circuit, and the switch 24 is raised to complete a shunt circuit for the resistor (5. The switch 2-1 then operates as a fluttering relay to fi'urther accelerate the motor.

When the motor has reached such a speed justed for such a generator voltage and such an excitation of the motor field winding as will produce the desired speed. It is only necessary, therefore, when this adjustment has been made, to open and close the main switch to cause the motor to be automati cally accelerated to the same speed which it had before it was stopped.

My invention may be used with particular advantage in connection with mechanisms where frequent stops are necessary and it is desirable to operate at the same normal speed without adjustments at each time of starting.

I claim'as my invention:

1. In a motor. control system, the combination with a motor, and a generator for supplying energy tothe motor, of a plurality oi electromagnetic switches operating at a predetermined value of current sup plied to said motor for gradually increasing the generator voltage to a normal. value and then gradually decreasing the tield excitation of said motor.

2. In a motor control system, the combination with a motor, and a generator in cir cuit therewith, of automatic means for gradually increasing the voltage of the generator to a normal value and then gradually decreasing the field excitation of said motor.

3. In a. motor control system, the combination with va generato' and a motor connected in series'relation, of means operating at a predetermined voltage of saidgcncrator for controlling the field excitation of the motor, and means o 'ierating in accordance with the value of the current supplied to said motor for controlling the voltage 01'' the generator.

4. In a motor control svstcin, the combination with a generator and a motor connected in series relation and provided with lield windings and resistors in circuit with said windings, of means controlled in accordance with the voltage of said generator for controlling -aid resistors.

5. In a motor control system, the combiof the current supplied to said motor for controlling the excitation of the motor fiehi In testimony whereof, I have hereunto Winding. subscribed my name this 26th day of May 10 6. In a motor-control system, the combi- 19M,

nation with a generator and a motor con- 5 nected in series relation, of means operating HOWARD BEACH at a predetermined voltage of said genera- Witnesses: tor for controlling the field excitation of the ORA A. COLBY, motor. B. B. HINES. 

